Willard Foxton is an investigative journalist & television producer. He writes on skulduggery wherever he finds it, especially in the world of technology.

The police haven't found a '3D-printed gun'. They've found a 3D printer

This Liberator pistol was the first firearm made with a 3D printer. (Photo: AFP)

This morning, the police are trumpeting the discovery of a "3D-printed gun factory" in Manchester. That's not what they've found at all – what they've found is just a 3D printer. By their logic, the could walk into brilliant 3D printing dollmaker MakieLab tomorrow and shut the whole thing down as "packed to the roof with gun-making machines".

Yes, the criminals in question were trying to make a gun, but they hadn't got anywhere near succeeding. They weren't building the successful "Liberator" design – in fact, what's being touted as a "magazine" looks suspiciously like a part from a Pez dispenser. The Liberator – the only reliable 3D printing gun design – doesn't carry a magazine.

I've spoken at length to Cody Wilson, the man who made the plans for the Liberator handgun – regular readers will be disappointed to hear that, despite me travelling to Austin to meet him, he's turned down my offer of being shot with the gun, as he "likes me too much to shoot me".

The way the Liberator design overcomes the limitations of 3D printing is it separates the barrel from the gun, meaning when the plastic inevitably splits under the heat and pressure of firing, the damage is much less likely to be fatal to the firer. Still, Cody did hundreds of tests while not holding the gun to make sure his design worked, testing different bullet calibres and chamber pressures. Designing a gun that worked was a huge feat – most manufacturing engineers thought it couldn't be done on home equipment.

And while the Liberator is a great piece of design, it's still not a very good gun. It's woefully inaccurate, even at short range. That's partly because the plastic barrel can't grip the bullet in the same way a metal one can. One of the reasons the insurance company was so nervous about Cody shooting me was we couldn't guarantee he'd hit my bulletproof vest, and not something more vital.

In a real gun, the bullet expands under the heat of firing, so the bullet is forced down the barrel, which is actually too small to fit the bullet down easily. That means most of the force goes behind the bullet, and the rifling in the barrel imparts the bullet a spin, which gives it accuracy.

In the plastic gun, the barrel isn't hard enough to resist the forces involved, so most of the energy of the gunpowder behind the bullet is lost. The bullets don't even hit that hard. To guarantee a fatally wounding shot, you'd have to push the gun into someone before you pulled the trigger. You'd have to use it like a knife.

In fact, with the Liberator being single-shot (you really want to replace the barrel each time you fire), the knife is arguably more useful as you can stab people several times.

Here's the point – the Liberator is about the best 3D printed gun and it's not that dangerous. Cody knows that – he based the design on a personal defence weapon for Allied agents in WW2. He knows it's inaccurate and lacks power. He largely made it to prove a point about gun control in the USA and why 3D printing makes it even more impossible.

The truth is, 3D printing is nowhere near the level where you can make guns with it that are comparable with modern firearms. The nature of the best home technology – which relies on fusing thermoplastic particles – means it is fundamentally incompatible with firearms, which by their nature generate tremendous pressure and heat.

Maybe in a decade we should worry, but for now, there's no danger from home 3D printing – it's great for making fun little widgets, or running a craft business from home, but not much else.